The present invention relates to a gear arrangement comprising a first and a second gearwheel, the invention further relates to a transmission provided with an inventive gear arrangement.
In order to reduce the noise emission from two gearwheels meshing with each other, they can be provided with helical gear teeth. A disadvantage of helical gears is that during torque transfer between the gearwheels, the helical gear engagement causes axial gear mesh forces. The axial gear mesh forces will give a resulting, thrust along the axis of the gearwheel. The gearwheel must thereby be accommodated by appropriate bearings in order to take up the axial thrust
Loose gearwheels arranged rotatably upon a shaft can be rotationally connected to each other and to the shaft by mechanical tooth clutches. This will be referred to as a stack of interconnectable loose gearwheels. This is common in dual clutch transmissions in order to limit the design to one countershaft.
Similarly, it is not uncommon in other types of transmissions to find stacks of interconnectable loose gearwheels that are rotatably arranged on bearings on a shaft and can selectably be rotationally locked to each other. One example is transmissions with a winding power flow, where the power is transferred back and forth more than once between two rotational axes.
In a stack of interconnectable loose gearwheels, at least one of the gearwheels can also be connected to the shaft. Torque can be transferred in different ways by means of selectable engagement of tooth clutches:                between the shaft and the gear mesh of one of the gearwheels in the stack        between the gear meshes of two adjacent gearwheels in the stack        between the gear meshes of two non-adjacent gearwheels via intermediate gearwheels in the stack (the intermediate gearwheels would then function as power-transferring sleeves)        
In the first case the shaft and the gearwheel in question will be rotationally locked. There will be no relative rotation between them, and the bearings that carry the gearwheel will not be subjected to any nominal life consumption.
In the second and third cases the two gearwheels with power-transferring gear meshes will be rotationally locked. In a general case they will rotate with a different speed than the shaft. So, the bearings that carry these gearwheels will be simultaneously subjected to loads from the gear mesh forces and relative rotation. This implies a consumption bearing life.
The bearing life of a stack of interconnectable loose gearwheels may be limiting for the overall durability of a transmission. In many cases it would not be possible to use stronger and larger bearings due to space limitations.
There is thus a need for an improved gear arrangement, which increases the lifecycle of the bearings within the gear arrangement.
It is desirable to provide an inventive gear arrangement with a longer lifecycle than previous known solutions.
The inventive gear arrangement comprises a first and a second gearwheel. The first and second gearwheels are arranged next to each other upon a first shaft such that said first and second gearwheels can rotate relative said first shaft. The gearwheels are thereby preferably arranged upon some kind of bearing arrangement, either as separate bearings or semi integrated bearings in which the outer ring is formed by a part of the inner surface of the gearwheels and/or the inner ring is formed by a part of the outer surface of the shaft.
The gear arrangement is characterised in, that at least one gearwheel of said first and second gearwheels is arranged upon said first shaft such, that it can be axially displaced between a distanced axial position and a contact axial position upon said first shaft. Further, in said distanced axial position, said first and second gearwheels are distanced from each other and in said contact axial position, an axial contact between said first and second gearwheel is enabled.
The inventive gear arrangement enables that, when the one gearwheel is positioned in the contact axial position, axial forces upon the one gearwheel directed towards the other gearwheel will be transferred to the other gearwheel. The axial loads upon the first and second gearwheels thereby cancel each other out. The axial load upon the bearings will be completely reduced or at least essentially reduced.
By using the inventive gear arrangement such, that the axial gear meshes forces from the first and the second gearwheel cancel each other out, when the first and/or the second gear wheel rotates relative the first shaft, the bearings do not have to be subjected to large axial load when they are subjected to rotation, whereby the lifecycle of the bearings upon which the gearwheels are mounted increases.
In a situation where there is no relative rotation between the gearwheels and the first shaft, i.e. no rotation in the bearings, the bearings can be subjected to axial load without any additional wear upon the bearings.
There are bearings that allow an axial displacement; the one gearwheel can be arranged upon such a bearing in order to facilitate the axial displacement of the one gearwheel. A bearing facilitating the axial displacement is preferably a needle, a cylindrical roller bearing or a toroidal roller bearing.
It is preferred that the at least one gearwheel is displaced into said contact axial position when it transfers a torque load. Gearwheels are subjected to axial forces when they are provided with helical gear teeth and transfer torque to another gearwheel meshing therewith. It is thereby provided that said at least one gearwheel is provided with helical gear teeth. The helical gear teeth is preferably directed such, that by transferring torque from or to the at least one gearwheel from a gearwheel meshing therewith, the at least one gearwheel is displaced in direction towards the other of the first and the second gearwheel, the direction is preferably chosen such, that the torque transfer direction that is most commonly used, is the one that causing the axial contact between the first and the second gearwheel.
In a preferred embodiment, both the first and the second gearwheels are arranged such upon said first shaft, that they both can be axially displaced between a distanced axial position and a contact axial position upon the first shaft.
It is further preferred that both said first and said second gearwheels are provided with helical gear teeth, whereby the helical gear teeth of said first gearwheel are cut in the same direction, i.e., have the same hand of helix, as the helical gear teeth of said second gearwheel. When the first and second gearwheels are locked to each other (and thereby rotate in the same direction and with the same speed) they will be pressed against each other due to the axial forces that arises when transferring, a torque to/from the gearwheels they are meshing with, when power is transferred in one direction between the first and second gearwheels and pressed away from each other when power is transferred in opposite direction.
It is preferred that the at least one gearwheel is mounted upon a first and a second bearing and that the at least one gearwheel can slide upon the first and second bearing. In order to provide a defined sliding distance, the at least one gearwheel is provided with an inwardly directed protrusion, whereby the at least one gearwheel is arranged such upon said first and second bearing, that the inwardly directed protrusion is placed between the first and the second bearing and thereby allows a defined axial displacement. Said protrusion may also be composed of a separate part, e.g., a retaining ring or a shoulder of a bearing outer ring, as would be known to a person skilled in the art.
In an alternative arrangement the defined sliding distance is provided by an outwardly directed protrusion, which is axially fixed to the first shaft, whereby the at least one gear wheel is axially fixed upon its bearings and the bearings are able to slide upon the first shaft. The axial relative motion is thereby limited by the outwardly directed protrusions upon the first shaft.
It is preferred that the gear arrangement is provided with a first synchronisation mechanism or a dog clutch enabling a rotational connection between said first and said second gearwheel. The first synchronisation mechanism ensures that the first and second gearwheel rotate in the same speed and direction, whereby the axial contact can does not interfere with the individual rotation of the first and second gearwheel.
It is further preferred that the gear arrangement is provided with a second synchronisation mechanism or a dog clutch, which enabling a synchronisation between one of said first and second gearwheel and said first shaft.
The inventive gear arrangement can be applied in a diversity of fields, and is especially useful in fields where a bearing failure or an exchange of bearings is critical and/or expensive. One such arrangement is a transmission and especially a dual-clutch transmission. The use of the inventive gear arrangement in a transmission increases the life cycle of a transmission and lowers its maintenance costs.
The gear transmission is preferably used in a transmission having a centre shaft and a countershaft, wherein said gear arrangement is provided upon said countershaft.
Preferably meshes at least said first gearwheel with a first primary gear teeth of said transmission and said second gearwheel with a gearwheel upon the centre shaft.